Vehicular headlights are designed to project high intensity beams of light in prescribed patterns over selected portions of a highway. Generally, vehicles are equipped with a pair of headlights for projecting so-called high beams of light to illuminate the entire width of the highway in front of the vehicle. A second pair of headlights projects a so-called low beam pattern that is directed downwardly and to the right of the high beam so as not to blind an oncoming motorist. In some vehicles, high and low beam patterns are projected from the same lamps using different filaments.
In order to produce the desired illumination, headlight lamps must be properly aimed and produce a particular light pattern. Standards for headlight aiming and illumination patterns are prescribed by industrial groups, such as the Society of Automotive Engineers (SAE), and by governmental agencies. Generally, different aiming and illumination pattern standards have been prescribed for different geographical areas, such as North America and Europe, making it difficult to produce a universally applicable aiming apparatus.
Devices and methods for determining proper vehicle headlight aiming during vehicle manufacture and after vehicles have been in use are known. Two examples of known methods and apparatus are described in U.S. Pat. Nos. 3,515,483 to Irwin and 4,435,078 to de Brabander et al. These known devices employ a lens to focus a headlight light beam within a compact electro-optical unit. A number of discrete light intensity sensors are disposed within the optical system for sensing the intensity of light at a relatively small number of positions in the light beam. In the '483 patent, the intensities of light detected by each of nine discrete light intensity sensors are compared in selected pairs to determine whether established aiming criteria are satisfied within a prescribed degree of accuracy. If not, the position of the headlight is adjusted to achieve the proper aim. This method of comparing the relative intensities of different portions of the light pattern is referred to as the fractional balance method. The '078 patent employs a variation of the fractional balance aiming technique. There, light intensities measured at about the same number of discrete points by discrete light intensity sensors are used directly, or after being multiplied by fractional constants, in various comparison tests to determine whether a headlight is accurately aimed or not.
While the known methods and devices are useful in accurately aiming vehicular headlights, the devices are specifically designed for use with a particular set of aming standards. That is, the known methods and devices are limited in flexibility. The known devices are not readily adaptable to different or changing aiming standards because they sense light intensities at a limited number of discrete locations in the headlight beam based on a particular standard. In addition, the known apparatus and methods are inadequate to assure that the light pattern emitted by a headlight meets industry and governmental standards. In an era of increasingly stringent governmental standards concerning headlight aiming and beam patterns, particularly for newly manufactured vehicles, it is important that a headlight aiming device provide accurate and rapid results, be adaptable to new standards and be capable of testing a headlight beam pattern in addition to aiming accuracy.
Accordingly, it is an object of the present invention to provide a vehicle headlight aiming method and device that is readily adaptable to different aiming standards.
Another object of the invention is the provision of a headlight aiming method and device that is not limited in performance by the specific locations of a limited number of discrete light intensity sensors.
Still another object of the invention is the provision of apparatus and methods for readily measuring headlight illumination pattern.
Yet another object of the invention is the provision of apparatus and methods for measuring both headlight aim accuracy and headlight illumination pattern.
A further object of the invention is the provision of an automatic headlight aiming method and device in which errors in headlight aiming can be rapidly and automatically corrected.
Another object of the invention is the production of a visual display of the illumination pattern of a headlight.